Place walnut sausage meat into a mixing bowl and add cheese plus the sautéed stem/apple/shallot/sage mixture. Stir until combined and mixture is completely moistened.
To make these mushrooms vegan, swap the cheddar for non-dairy cheddar shreds or nutritional yeast
For a quick seasoning for the walnut sausage, use 1 TB Wildtree Sausage Seasoning Blend
If you happen to have any leftover filling, shape them into patties and make vegetarian breakfast sausages
MAKE AHEAD OPTION:
If making in advance, stuff the mushrooms and cover with plastic wrap. They will keep 1-2 days before baking. Or you can store the filling separately and stuff the mushrooms the day you plan to serve these up. If you are going right from the fridge to the oven, add another 10-15 minutes of cooking time on, as the cold mushrooms will need more time to cook.